A system identification device according to the related art identifies an inertia moment of a control target by dividing, by an integral time of an integrator, a steady-state value of a command torque difference Nth-order integral value to be an Nth-order time integral value of a signal obtained by subtracting an equivalent IP control system command torque from a PI control system command torque (see e.g., Patent Document 1).
FIG. 8 is a block diagram showing a system identification device according to the related art.
In FIG. 8, 801 denotes a first mixer, 802 denotes a proportional amplifier, 803 denotes an integrator, 804 denotes a second mixer, 805 denotes a control target, 806 denotes a control target Coulomb friction, 807 denotes a first-order lag filter, and 808 denotes an Nth-order integration.
A structure and operation of the system identification device according to the related art will be described below with reference to FIG. 8.
The first mixer 801 outputs a signal obtained by subtracting a speed from a speed command. The proportional amplifier 802 inputs the output of the first mixer 801 and outputs a signal obtained by amplifying the input signal. The integrator 803 inputs  the output of the proportional amplifier 802 and then outputs a PI control system command torque to be a value obtained by adding the input signal and a 1st-order time integral value amplification value of the input signal. The second mixer 804 outputs a value obtained by adding the PI control system command torque and an output of the control target Coulomb friction 806. The control target 805 inputs the output of the second mixer 804 and then outputs the speed. The control target Coulomb friction 806 inputs the speed and then outputs a signal having a constant absolute value and a reverse sign to that of the input signal. The first order lag filter 807 inputs the PI control system command torque and then outputs an equivalent IP control system command torque. The Nth-order integration 808 inputs a signal obtained by subtracting the equivalent IP control system command torque from the PI control system command torque and then outputs a command torque difference Nth-order integral value to be an Nth-order time integral value of the input signal.
As described the above structure, a steady-state value of the command torque difference Nth-order integral value for the speed command having a constant sign is divided by the integral time of the integrator 803 to identify an inertia moment of the control target 805.
Patent Document 1: JP-A-7-333084 Publication (Page 8, FIG. 8(a))